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Tone and volume control stages
Cutting out harsh high frequency harmonics seems to be one of the underlying principles of the TS series. Following the clipping stage there is a 1K resistor leading to a 0.22uF capacitor to ground. This acts like a simple RC lowpass filter, with the rolloff point being 723Hz. This means that the output of this stage is down 20db (10:1) at 7230 Hz, and another 6db (20:1) at 14KHz, close to the top of the audio range. From this simple lowpass filter, the signal goes to the active tone control stage. The control is a 20K potentiometer strung from the (-) to the (+) input of the second opamp section. The wiper of the control is tied to a series RC combination to ground. This RC is a 220 ohm resistor and a 0.22uF capacitor. As a series network, at frequencies above the point at where the capacitive impedance is less than 220 ohms (which happens at about 3.2KHz), the network just looks like the 220 ohm resistor. At frequencies below that point, the capacitor impedance gets larger as the frequency goes down until at some point the capacitor impedance is large even compared with the full resistace of the tone control (20K); this happens at about 36Hz, below guitar frequencies.
The tone control operations are easiest to see if you assume that the tone control is at one end or the other of its range. When fully toward the (+) end, the capacitor shunts the frequencies above 3.2KHz to ground; when fully toward the (-) end, the capacitor shunts feedback frequencies above 3.2KHz to ground. This means that at the (+) side, the signal gets another -6db/octave high frequency rolloff, while when it's at the (-) side the signal finally gets some treble boost, +6db/octave above 3.2KHz. Note that the "boost" actually just levels off the -6db/octave induced by the 1K/0.22uF network ahead of the active control stage, so the treble is just not being cut any more above the turnover frequency for the tone control stage when fully at "treble".
